Implement Passkey to third party Password Manager

Question

I am trying to implement the Passkey in my Password Manager App using the code below to generate Passkey for different website. However, what concerns me is that my password manager generates a Passkey for different websites when a user requests it. How can I manage the associated domain?

here its my code, for now it gives error, If I generate from google website:

 func signUpWith(userName: String, anchor: ASPresentationAnchor) {
        self.authenticationAnchor = anchor
        let publicKeyCredentialProvider = ASAuthorizationPlatformPublicKeyCredentialProvider(relyingPartyIdentifier: domain)

        // Fetch the challenge from the server. The challenge needs to be unique for each request.
        // The userID is the identifier for the user's account.
        let challenge = Data()
        let userID = Data(UUID().uuidString.utf8)

        let registrationRequest = publicKeyCredentialProvider.createCredentialRegistrationRequest(challenge: challenge,
                                                                                                  name: userName, userID: userID)

        // Use only ASAuthorizationPlatformPublicKeyCredentialRegistrationRequests or
        // ASAuthorizationSecurityKeyPublicKeyCredentialRegistrationRequests here.
        let authController = ASAuthorizationController(authorizationRequests: [ registrationRequest ] )
        authController.delegate = self
        authController.presentationContextProvider = self
        authController.performRequests()
        isPerformingModalReqest = true
    }